The subject-matter of the invention is a draw-off nozzle in an open-end spinning machine.
To produce a yarn by spinning, it is known to arrange a stationary draw-off nozzle in front of a rapidly rotating open-end rotor, in the rotational axis.
In a manner known in itself, the filaments are fed into the rotor where they lie on the inclined face of the rotor, form the yarn in the rotor notch, pass out of the rotor notch in the radially inwards direction and enter the stationary draw-off nozzle in the region of the rotational axis.
The purpose of the draw-off nozzle is to deflect the inherently twisted yarn leaving the rotor notch, and also to develop a false twist so that the spinning process remains stable.
It is known that such draw-off nozzles can be formed from a metallic material, a ceramic material, or a metal/ceramic composite.
To promote the propagation of the yarn twist into the rotor groove, it is known to form one or more notches in the wall of the lead-in funnel defining the draw-off nozzle. It is known to give such a notch a symmetrical cross-section, that is to say one where the entry wall and the impingement wall have precisely the same form, so that the result is a V-shaped, completely symmetrical notch.
Draw-off nozzles with symmetrical notch configurations which have hitherto existed on the market have notches with aperture angles ranging from 50xc2x0 to 65xc2x0, depths of between 0.2 and 0.45 mm, and positioning angles in relation to the axis of from 10xc2x0 to nearly 90xc2x0.
Moreover it is known to provide at least 3 such notches, and indeed 4, 6, 8 or 12 such notches, distributed around the circumference of the lead-in funnel.
A drawback of the known symmetrical notch configurations is that the incoming yarn takes up position randomly within the notch. Depending on the spinning conditions, it can even happen that the yarn does not find its way into the notch at all, but leaps over it in a haphazard manner.
Therefore the fundamental problem which the invention sets out to solve is to perfect the grabbing notches in a draw-off nozzle of the kind stated in the introduction so that, irrespective of the spinning conditions, every notch comes into play in a uniform manner, thus increasing spinning stability.
For the solution of the stated problem, the invention is characterized by the technical caching of claim 1.
The essential feature of the invention is that each grabbing notch has an entry wall raked at a shallower angle than the impingement wall adjoining it on the other side of the root of the notch.
Thus the invention proposes for the first time a grabbing notch that is asymmetrical, i.e. effectively tilted or angled towards the yarn entry side.
The essential benefit yielded by this technical teaching is that the entry wall on the entry side as it were advances to meet the yarn. The yarn dips smoothly on to the entry wall, which slopes in the yarn entry direction and guides the yarn to the root of the notch, where it is stopped abruptly; after the yarn has left the root of the notch, it is led back up the impingement wall, and so out of the notch.
Thus the significant feature of the present invention is that the skew of the grabbing notch towards the yarn entry side ensures that the yarn moves smoothly and steadily across the entry wall towards the root of the notch (incidentally undergoing braking as it does so), before running on to the impingement wall, and then leaving the notch again.
This has not been the case in the known state of the art. Because the entry wall was set at a sharp angle to the yarn entry direction, the yarn tended to leap over the entry wall altogether, and then to abruptly hit a steeply raked surface of the impingement wall (e.g. in the upper third of the impingement wall), so that the braking effect was unfavourable, and this sudden overleaping of the grabbing notch gave rise to high tension peaks in the yarn. The invention avoids these.
For the provision of a grabbing notch according to the invention there exist various possible embodiments, all of which are claimed as essential to the invention.
In a first embodiment of the present invention, the notch wall on the entry side is profiled essentially as a straight line which at its entry (i.e. radially outward) end meets the spherically curved lead-in wall of the funnel at a slight angle i.e. with a slight discontinuity. Advantageously a tangential transition to the free-formed surface of the nozzle occurs at at least one point of the entry side envelope.
In a second configuration, the entry wall of the notch, instead of being straight, has a spherical curvature (a convex curvature), and merges smoothly with the convex lead in wall of the funnel, which also has a spherical curvature. In this second embodiment there is no perceptible transition between the lead-in wall of the funnel and the wall of the notch on the entry side; in other words, a tangential transition prevails at all points.
In a third possible embodiment, the entry wall of the notch is not convex, but concave, and adjoins the spherically curved, convex lead-in wall at a discontinuous transition point, so that the wall on the entry side of the notch is saddleshaped for example.
The invention therefore relates to all transition states between the three stated extreme forms of the entry wall of the notch, namely the convex wall, the straight wall and the concave wall, tangential transitions on the entry side being advantageous and recommended. The markedness of the notch in its envelope is highly dependent on the radii defining the lead-in funnel.
At the radially inwards side of the notch wall lies the root from which the impingement wall rises on the exit side of the notch. A significant feature here is that the angle of the impingement wall to the perpendicular is greater than the angle of the entry wall to the perpendicular.
Thus the angle of entry can be in the range of say 50xc2x0 to 65xc2x0 to the perpendicular owing to the greater tilt of the entry wall of the notch, whereas the impingement wall on the exit side will have an angle in the range of say 10xc2x0 to 30xc2x0. This angle is also called the stop angle.
The invention provides that the material of the lead-in funnel can be metal or ceramic or a metal/ceramic composite. Other materials, such as for example coated plastic material, coated metal, or similar, can also be used.
A notch depth of 0.1 to 0.4 mm, depending on the notch intensity required, is preferred; and an odd number of notches, such as 3, 5, 7, 9, 11 or 13 notches, uniformly disposed around the circumference of the lead-in funnel, is particularly preferred.
A notch positioning angle of 30xc2x0 (xc2x15xc2x0) is preferred. Rotor yarns are generally spun as Z-twist yarns. For the draw-off nozzle, this means that the yarn rotates anticlockwise when viewed in the yarn draw-off direction (that is looking down on the mouth of the nozzle from above), as indicated in FIG. 2. Accordingly, the stopping side of a notch should be located on the left of the root of the notch, and the entry side on the right; or, in the case of S-twist, the other way round. As already mentioned herein, the notch root should also lie on a straight line wherever possible, which is a first preferred configuration. In another configuration, the notch root has a spherically arched and convex form.
As already mentioned herein, the notch root should also lie on a straight line wherever possible, which is a first preferred configuration. In another configuration, the notch root has a spherically arched and convex form.
All details and features disclosed in the documents including the abstract, and in particular the embodiment illustrated in the drawings, are claimed as essential to the invention in so far as, individually or in combination, they are novel with respect to the state of the art.
The invention will now be described in detail with reference to drawings illustrating a number of ways of carrying out the invention. Further essential features and advantages of the invention will become apparent from the drawings and from the description thereof.